Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, charged-coupled devices (CCDs), solar cells, and digital micro-mirror devices (DMDs).
Semiconductor devices perform a wide range of functions such as signal processing, high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual projections for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Semiconductor devices exploit the electrical properties of semiconductor materials. The atomic structure of semiconductor material allows its electrical conductivity to be manipulated by the application of an electric field or base current or through the process of doping. Doping introduces impurities into the semiconductor material to manipulate and control the conductivity of the semiconductor device.
A semiconductor device contains active and passive electrical structures. Active structures, including bipolar and field effect transistors, control the flow of electrical current. By varying levels of doping and application of an electric field or base current, the transistor either promotes or restricts the flow of electrical current. Passive structures, including resistors, capacitors, and inductors, create a relationship between voltage and current necessary to perform a variety of electrical functions. The passive and active structures are electrically connected to form circuits, which enable the semiconductor device to perform high-speed calculations and other useful functions.
Semiconductor devices are generally manufactured using two complex manufacturing processes, i.e., front-end manufacturing, and back-end manufacturing, each involving potentially hundreds of steps. Front-end manufacturing involves the formation of a plurality of die on the surface of a semiconductor wafer. Each semiconductor die is typically identical and contains circuits formed by electrically connecting active and passive components. Back-end manufacturing involves singulating individual semiconductor die from the finished wafer and packaging the die to provide structural support and environmental isolation. The term “semiconductor die” as used herein refers to both the singular and plural form of the words, and accordingly can refer to both a single semiconductor device and multiple semiconductor devices.
One goal of semiconductor manufacturing is to produce smaller semiconductor devices. Smaller devices typically consume less power, have higher performance, and can be produced more efficiently. In addition, smaller semiconductor devices have a smaller footprint, which is desirable for smaller end products. A smaller semiconductor die size can be achieved by improvements in the front-end process resulting in semiconductor die with smaller, higher density active and passive components. Back-end processes may result in semiconductor device packages with a smaller footprint by improvements in electrical interconnection and packaging materials.
In a conventional Fo-WLCSP, a semiconductor die with contact pads is mounted to a carrier. An encapsulant is deposited over the semiconductor die and the carrier. The carrier is removed and a build-up interconnect structure is formed over the encapsulant and semiconductor die. The electrical interconnection between a Fo-WLCSP containing semiconductor devices on multiple levels (3-D device integration) and external devices can be accomplished by forming redistribution layers (RDLs) within a build-up interconnect structure over both a front side and a backside of a semiconductor die within a Fo-WLCSP. The formation of multiple RDLs including over a front side and backside of a semiconductor die can be a slow and costly approach for making electrical interconnection for 3-D Fo-WLCSPs and can result in higher fabrication costs. Furthermore, the RDLs of build-up interconnect structures are prone to cracking and warping under stress, which can propagate through the RDLs to the semiconductor die and contact pads causing defects in the electrical interconnection. Conductive interconnect structures can be formed within the Fo-WLCSPs and electrically connected to the RDLs to provide vertical electrical interconnection for 3-D device integration. Conductive interconnect structures formed within Fo-WLCSPs can have poor electrical and mechanical connectivity with the RDLs. Additionally, the process of forming conductive interconnect structures can reduce structural support for the RDLs, particularly when openings are formed in the package over the RDLs. Forming build-up interconnect structures and conductive interconnect structures within Fo-WLCSPs can also lead to warpage before and after removal of the carrier.